Diffusion chamber (DC) culture studies are being performed to test the reliability and reproducibility of the system for study of human hemopoietic cells. Two types of chamber materials, Nuclepore (NDC) and Millipore (MDC), are being evaluated. The preliminary results of cultures of the blood cells of 5 normal volunteers indicate the presence of pluripotent and/or committed stem cells since erythro-, granulo- and megakoryopoiesis were noted. Although the pattern of cell recovery was similar from the two types of DC's, the total cell yield was higher from NDC's than from the MDC's. Preliminary data from marrow and/or blood cell cultures of 5 patients with myelofibrosis with myeloid metaplasia suggest that the blood and marrow of these patients contain an increased number of erythro and granulocytic progenitors. Granulocyte mobilization from the marrow into the blood and its proliferation in the marrow are postulated to be regulated through leukocytosis mobilizing factor (LIF) and colony stimulating factor (CSF) respectively. Peritoneal leukophoresis with starch in dogs is associated with rapid mobilization of the granulocytes from the marrow into the blood and increased marrow granulocytopoiesis. The cell-free peritoneal fluid is found to have both in vitro CSF and in vivo LIF activities. Studies are now being performed to see whether these two activities reside in the same or different moieties.